Heat oil in Dutch oven. Liberally season the roast with Beazell's Cajun Seasoning on all sides. Sear the roast in oil until well browned on all sides. Remove roast and set aside.

Add flour to oil and make a medium brown roux – stirring constantly. Add diced onions and cook until they are translucent. Add beef broth and mushrooms. Stir together, scraping the bottom of the pan for the browned bits from the roast. Return roast to Dutch oven. Cover and simmer on medium-low stirring occasionally for 3 to 3 1/2 hours. Add additional Beazell's Cajun Seasoning to taste.

Remove the roast and slice. Serve roast over rice (or mashed potatoes) and top with the onion mushroom gravy.